The present invention relates to a gas turbine disk material suitable for a gas turbine used as a motor in power plants.
In general, steam turbines are widely used as a motor for the main power generation in power plants in view of thermal economy. Recently, gas turbines have come to be widely used in view of environmental problems and good operability. Such gas turbines are activated at or around normal temperature and operated under high load. Accordingly, a material for gas turbine disks is required to have excellent strength and toughness in a temperature range between normal temperature and high temperature and excellent high-temperature creep characteristics which ensure a small reduction in strength in operation at high temperature.
As a material for such gas turbine material are used 12Cr-type heat resisting steels containing 8 to 12 percent by weight (hereinafter, merely "wt %") of chromium such as M152 (the composition thereof corresponds to a sample B1 in TABLE-1 later). The gas turbine disk materials of this type contain nickel to ensure toughness and contain molybdenum and vanadium in addition to chromium for a solid-solution hardening of a base construction and for a better dispersion by carbides of the respective elements, thereby improving high-temperature creep characteristics to be used for a gas turbine operated at about 400.degree. C.
In recent years, power is generated in power plants at higher temperature and under higher pressure in order to improve a thermal efficiency. Thus, there is a demand for a gas turbine disk material which has excellent creep characteristics even at a high temperature exceeding 500.degree. C.
However, a textural change is likely to occur at high temperature in existing heat resisting steels having a high chromium content such as M152, thereby causing a reduction in creep strength. Thus, such conventional gas turbine disk materials reduce the reliability of power plants in the case of operations in a thermal environment from normal temperature to 500.degree. C. or above.